The present invention relates to a display apparatus, and more particularly, to a coordinate input display apparatus which includes a transparent digitizer.
A coordinate input display apparatus equipped with a liquid crystal display (LCD) as a display unit and a digitizer (tablet) as a coordinate input device have been developed in which the input device is provided in a single body on the LCD.
FIG. 1 schematically shows a conventional coordinate input display apparatus. A transparent digitizer 21 is disposed, with a predetermined clearance 23, over a display unit 22, such as an LCD or the like. The digitizer 21 is a resistance film sensitive type. Coordinates are input by depressing the digitizer 21 with a coordinate input pen 24 or an operator's finger.
A read controller 25 connected to the digitizer 21 reads the input coordinates and sends the coordinate data to a main system 26. The main system 26 processes the coordinate data and generates display data to be displayed on the display unit 22 as needed. A display controller 27 performs display control on the display unit 22 based on the display data from the main system 26. When a line L1 is input on the digitizer 21 by, for example, the coordinate input pen 24, the read controller 25 reads the coordinates of multiple points of the line L1. The main system 26 generates display data based on the read coordinate data. Based on the display data, the display controller 27 displays a line L2 corresponding to the line L1 on the display unit 22.
The digitizer 21 is moved or bent by the depression load of the coordinate input pen 24. When the amount of bending of the digitizer 21 is too large, the bottom of the digitizer 21 contacts the display unit 22. In this case, the depression load acting on the digitizer 21 is transmitted to the display surface of the display unit 22 and may adversely affect image display on the display unit 22.
When the display unit 22 is an LCD, particularly, contacting the display surface causes critical display disturbance called an interference fringe. For this reason, the clearance 23 is generally provided so that the digitizer 21, even when bent, does not contact the surface of the LCD. To reduce the bending amount of the digitizer 21, the thickness of the digitizer 21 is set large.
Making the digitizer 21 thicker or setting the large clearance 23 between the digitizer 21 and the display unit 22 increases the parallax, making pen inputs or finger-touching inputs difficult. The parallax is a distance between the surface on which a user actually makes inputs with the pen 24 and the surface where dots corresponding to the inputs are displayed. When the user obliquely observing the input surface designates a specific position on the input surface with the pen 24, an image corresponding to that input is displayed on the display surface directly below the designated position. When the user the designated position, however, the image is not displayed on the display surface on an extending line which connects the user's eyes to the designated position. The user therefore notices some deviation between the input position and the display position. That is, the coincidence between the input position and the display position is impaired.
It is necessary to satisfy the competing, contradictory requirements of increasing the thickness of the digitizer 21 or the clearance 23 between the digitizer 21 and the display unit 22 and of decreasing those values in view of their influence on the parallax,
In the conventional coordinate input display apparatus, the thickness of the digitizer 21 and the clearance 23 between the digitizer 21 and the display unit 22 are determined empirically. However, the empirical determination lacks preciseness and does not necessarily provide optimal values.
Accordingly, it is an object of the present invention to provide a coordinate input display apparatus optimal values of the thickness of a digitizer and a clearance between the digitizer and a display unit.